Abelisauroids are the
most abundant theropods in the Cretaceous beds of Patagonia. They are
traditionally subdivided into large-sized Abelisauridae and smaller
Noasauridae. Here, we describe a new specimen of the small enigmatic abelisauroid
Velocisaurus unicus Bonaparte, 1991,
which was previously known from a single incomplete specimen from Neuquén City,
Neuquén Province, Patagonia. The new material comes from the Santonian Bajo de
la Carpa Formation (Late Cretaceous) at the Paso Córdoba locality, Río Negro
Province. It comprises an almost complete left hind limb and offers novel
information about the anatomy of this poorly known abelisauroid. The new
material shows that Velocisaurus is remarkable in having a very short, stout,
and anteriorly bowed femur, which has a notably subtriangular cross-section at
its proximal end. The tibia is long and slender, and the anterior surface of
the distal end is anteroposteriorly flat and transversely expanded, with an
enlarged surface for the ascending process of the astragalus. The pes has a
stout third metatarsal, rod-like metatarsals II and IV, and highly modified
phalanges of digit IV. The unique combination of characters of Velocisaurus indicates
that this taxon belongs to a still poorly understood radiation of
gracile-limbed abelisauroids. The inclusion of Velocisaurus in a comprehensive phylogenetic analysis recovers a
monophyletic Noasauridae, but with only very weak support. Detailed analysis of
features supporting the inclusion of Velocisauruswithin Noasauridae is discussed, and their implications for abelisauroid
phylogeny are revisited.